Third Generation, wide-area wireless data networks (“3G networks”) are being deployed throughout the world.
In 3G networks, Proportional Fair scheduling (“PF”) is a process used by base stations (BSs) to schedule downlink traffic flows to users (e.g., mobile/wireless devices) in a somewhat even-handed or fair manner. One example of how the PF process works is as follows. Consider a situation where the condition of a channel used by each active user sharing the channel is independently variable. To report the condition it detects, each user continuously sends its measured channel condition back to a centralized PF scheduler which resides within a base station. Provided the time it takes to send these measurements is relatively small compared to the rate at which the condition of the channel is varying, the scheduler receives a good estimate of the channel conditions detected by each user; information it then uses to schedule the transmission of packets to each user. PF is said to exploit multi-user diversity by selecting the user associated with the best channel condition to transmit to during a given time period/slot. By “multi-user diversity” we mean, for example, in a large system with multiple users each with an independently fading channel, there is more than likely at least one user that is associated with a channel whose condition is acceptable. This approach may substantially increase a wireless system's throughput compared to a so-called round-robin scheduler. However, it may be unfair to a user that is associated with a channel whose condition is not very good because few data/packets may be transmitted to such a user. Realizing this, alternative PF techniques attempt to assign a “weight” (e.g., a value) to each user that is based on a historical, average data rate achieved by a user over a given channel instead of using a instantaneous (i.e., real-time or current) rate.
Even though the alternative PF scheduling techniques may achieve high throughput and maintain some kind of fairness among users associated with the same base station, the degree or level of fairness achieved is still not acceptable and, in the inventors' opinion, can be improved.
Hindering the ability to achieve better or increased fairness is the fact that users and their devices (the terms are used interchangeably herein) are initially associated with base stations without taking into account fairness considerations. Instead, a mobile device is most commonly associated with a base station from which it receives the strongest signal. Such a user-to-base station association technique may create load imbalances (e.g., some base stations are heavily loaded while other neighboring base stations are lightly loaded) which tend to decrease the overall throughput and fairness for each user associated with a given neighboring base station.
Accordingly, it is desirable to provide methods and devices for achieving proportional fairness by taking into account user-to-base station associations.